Again, you can't cover everything, but you can force trolls and such to do it themselves. When you have slavery as a legalized thing, especially in this sort of game, there's absolutely going to be people asking "How much for a slave?" and that's a question you want to avoid.
And you still can play that in your old campaigns, but I'm not sure that given what Wizards and D&D is now that it would be prudent. There are definitely games meant to deal with that sort of topic, but I don't know if D&D is the best one given how wide the audience is.
So I helped Kickstart a Delta Green campaign called God's Teeth which absolutely includes amount child abuse and animal abuse. Of course, that game goes out of its way to talk about that stuff and explain it and present it in the most horrifying way possible, while also making it the mission to destroy that s***. But that's because Delta Green's gameplay is focused around destroying that stuff, unlike D&D which is basically a sandbox.